11-ch18 - spinal cord and spinal nerves - spinal cord and spinal... · external anatomy of the...

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Copyright 2009 John Wiley & Sons

Chapter 18

The Spinal Cord and the Spinal Nerves


Introduction – Spinal Cord

� Contains neural circuits that control some of your quickest reactions to environmental changes.

� Site for integration of neuronal stimulation that arises locally or from the PNS and the brain.

� Relays sensory nerve impulses headed for the brain, as well as motor nerve impulses from the brain to skeletal muscles and other effectors.

� The spinal cord is continuous with the brain and together they constitute the central nervous system (CNS).


Spinal Cord (Fig. 18.1a)

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Spinal Cord•Spinal meninges- cover the spinal nerves to the

intervertebral foramina exit point.

•Cerebrospinal fluid- a shock absorber and suspension system for the spinal cord and brain.

•Denticulate ligaments - thickenings of the pia mater

•project and fuse with the arachnoid mater and inner surface of the dura mater

•between the anterior and posterior nerve roots of spinal

nerves on either side.


Meninges

� Dura mater- most superficial- dense, irregular connective

tissue.

� Epidural space- cushion of fat and connective tissue

between the dura mater and the wall of the vertebral canal.

� Arachnoid- middle meninx- avascular covering- spider’s web

arrangement of delicate collagen fibers and some elastic

fibers.

� Subdural space- between the dura and arachnoid mater-contains interstitial fluid.

� Pia mater- innermost meninx- thin transparent connective

tissue layer that adheres to the surface of the spinal cord and brain.

� Subarachnoid space- between the arachnoid and pia mater-

contains CFS


Transverse section of the spinal cord

within a cervical vertebrae (Fig. 18.1b)

insert figure 18.1b

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External anatomy of the spinal cord and

spinal nerves. (Fig. 18.2a)


External Anatomy of the Spinal Cord

� Adult spinal cord length - 42 to 45 cm (16 –18 in.).

� Diameter about 2 cm (0.75 in.) in the mid-thoracic region.

� The cervical enlargement - from the fourth cervical vertebra to

the first thoracic vertebra.

� The lumbar enlargement - from the ninth to the twelfth thoracic

vertebra.

� Conus medullaris- tapering, conical structure at end of cord.

� ends at the intervertebral disc between the first and second lumbar vertebrae in adults.

� arising from the conus medullaris is the filum terminale.


Internal Anatomy of the Spinal Cord

� Two grooves divide the white matter into right and left sides.

� Anterior median fissure- wide groove on the anterior

(ventral) side.

� Posterior median sulcus- narrow groove on the posterior (dorsal) side.

� Gray matter- is shaped like the letter H or a butterfly and is

surrounded by white matter.

� Cell bodies of neurons, neuroglia, unmyelinated axons, and

dendrites of interneurons and motor neurons.

� White matter- bundles of myelinated axons of sensory

neurons, interneurons, and motor neurons.

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� Gray Commissure- forms the crossbar of the H.

� Central Canal- center is a small space- extends the length

of the spinal cord and contains cerebrospinal fluid.

� Horns- divisions of the gray matter on each side of the cord

� Anterior (ventral) gray horns- somatic motor nuclei (clusters of cell bodies)

� provide nerve impulses for skeletal muscle contraction.

� Posterior (dorsal) gray horns- cell bodies and axons of

interneurons and axons of incoming sensory neurons.

� Lateral gray horns- only in thoracic, upper lumbar, and

sacral segments of the spinal cord.

� autonomic motor nuclei that regulate activity of smooth

muscle, cardiac muscle, and glands.


Internal anatomy of the spinal cord

(Fig. 18.3a)

Nervous System 3 12

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Nervous System 3 13



� The white matter, like the gray matter, is organized into regions. The anterior and posterior gray horns divide the white matter.

� Anterior to the gray commissure is the anterior (ventral) white commissure, which connects the white matter of the right and left sides of the spinal cord.

� Columns- white matter divisions

� Posterior and Lateral White Columns

� Bundles of axons

� Tracts- carry information to and from specific regions

� Sensory and motor tracts



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Branches of typical spinal nerve (Fig.

18.4a)


Anterior view and oblique section of the

spinal cord (Fig.18.4b)


Spinal Nerves� Spinal nerves and the nerves that branch from them are

part of the peripheral nervous system (PNS).

� They connect the CNS to sensory receptors, muscles, and glands in all parts of the body.

� There are 31 pairs of spinal nerves. Each pair of spinal nerves arises from the spinal cord.

� There are 8 pairs of cervical nerves (C1–C8), 12 pairs of thoracic nerves (T1–T12), 5 pairs of lumbar nerves (L1–L5), 5 pairs of sacral nerves (S1–S5), and 1 pair of coccygeal nerves (Co1).

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Branches of the Spinal Nerves

� Posterior Root Ganglion- cell bodies

� Spinal nerve trunk- mixed nerve

� sensory posterior root and motor anterior root project

laterally from the spinal cord and converge.

� Ramus- trunk branches into two large branches

� becomes a series of smaller branches


Branches of the Spinal Nerves � Anterior (ventral) ramus and posterior (dorsal) ramus,

are somatic branches in the musculoskeletal system.

� Posterior (dorsal) ramus- serves the deep muscles and skin of the posterior surface of the trunk.

� Anterior (ventral) ramus serves the muscles and structures

of the upper and lower limbs and the muscles and skin of the lateral and anterior regions of the trunk.

� Smaller visceral branches (meningeal branch and the communicating rami) form the autonomic pathways to smooth muscle and glandular tissue.


Plexuses

� Axons from the anterior rami of spinal nerves, except for thoracic

nerves T2–T12, do not go directly to the body structures they supply

� Form cervical plexus, brachial plexus, lumbar plexus, and sacral

plexus. A smaller coccygeal plexus is also present.

� Groups of nerves emerge from the plexuses.

� T2-T12 form Intercostal or Thoracic nerves

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Cervical Plexus (Fig. 18.5a)


Brachial Plexus (Fig. 18.6a)


Lumbar Plexus (Fig. 18.7a)

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Sacral and Coccygeal Plexuses

�The anterior rami of spinal nerves L4–L5 and S1–S4 form the sacral

plexus.

• This plexus is situated largely anterior to the sacrum.

• The sacral plexus supplies the buttocks, perineum, and lower

limbs.

• The sciatic nerve arises from the sacral plexus.

• Coccygeal nerves form the small coccygeal plexus (S4-S5)


Sacral plexus (Fig. 18.8a)


Dermatomes

•Each spinal nerve contains sensory

neurons that serve a specific, predictable

segment of the body.

•Dermatomes are the areas of the skin that

provides sensory input to the CNS via one

pair of spinal nerves.

•The nerve supply in adjacent dermatomes

overlaps somewhat.

•Knowing which spinal cord segments

supply each dermatome makes it possible

to locate damaged regions of the spinal

cord

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Connective tissue coverings of a spinal

nerve (Fig. 18.10 a)


Connective Tissue Coverings of Spinal

Nerves

� Nerve fiber- axon and its associated glial cells

� Endoneurium- Each nerve fiber sits in a loose connective

tissue

� mesh of collagen fibers, fibroblasts, and macrophages

surrounded by endoneurial fluid (extracellular fluid) derived

from the capillaries

� nourish neurons, allows environment for action potentials

Connective Tissue Coverings of

Spinal Nerves� Perineurium- A thicker sheath of connective tissue that

packages nerve fibers into bundles called fasciculi.

� sheaths with up to 15 layers of fibroblasts distributed in a

meshwork of collagen.

� Diffusion barrier-blood brain barrier, osmotic pressure

maintained

� Epineurium- Outer sheath

� Bundles fascicles to form one nerve

� Fibroblasts and thick collagen

� Protects the nerve


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Sensory and motor tracts (Fig.18.11)

Tracts and Columns

� White Matter Tracts- sensory to brain, motor from brain

� Gray Matter- receives and integrates

information from white matter

� Tracts - Named for where they come from and where they go to


Sensory Tracts and Columns

� Lateral and Anterior Spinothalamic Tract-

� Sensation for pain, coolness, itch, tickle, deep

pressure, diffuse touch

� Posterior Columns-

� Proprioception, discrimination touch, two point discrimination, light pressure, vibration


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Motor Tracts and Columns

� Lateral Corticospinal, Anterior Corticospinal, and Corticobulbar Tracts-

� Control voluntary muscles

� Rubrospinal, Tectospinal, Vestibulospinal Tracts-

� Control automatic movements (postural muscles)



Reflexes and Reflex Arcs� Spinal cord serves as an integrating center for some

reflexes.

� Reflex- is a fast, involuntary, unplanned sequence of

actions that occurs in responseto a particular stimulus.

� Some reflexes are inborn, while other reflexes are

learned or acquired.


Reflexes and Reflex Arcs

� Spinal reflex- integration in the spinal cord gray matter,

� Knee jerk

� Cranial reflex- integration in the brain stem

� Tandem eye movement when reading

� Somatic reflexes involve contraction of skeletal muscles.

� Autonomic (visceral) reflexes generally are not consciously perceived.

� Smooth muscle, cardiac muscle, or glands

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� Sensory receptor- Responds to a specific type of stimulus by

generating one or more nerve impulses.

� Sensory neuron- Conduct from the sensory receptor along the axon of a sensory neuron to its axon terminals, located in the CNS

gray matter. Axon branches also relay nerve impulses to the brain,

allowing conscious awareness that the reflex has occurred.

� Integrating center- One or more regions of gray matter in the CNS act as an integrating center.

� Motor neuron- Impulses triggered by the integrating center pass out

of the spinal cord along a motor neuron to the part of the body that

will respond.

� Effector- The part of the body that responds to the motor nerve impulse, such as a muscle or gland.

Reflexes and Reflex Arcs


Patellar reflex (Fig. 18.12)

11-ch18 - spinal cord and spinal nerves - spinal cord and spinal... · external anatomy of the...

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